The present invention relates to a method of preparing arylacetic acid alkyl esters.
Several processes are known for the preparation of phenylacetic acid esters. Thus, phenylacetic acid esters may be obtained through the reaction of benzyl chloride with alkali cyanide followed by saponification of the nitrile to the acid, and subsequent esterification (Ullmann, 1953, Vol. 4,291). What is unsatisfactory in this process is the plurality of steps in the reaction. Phenylacetic acid esters may also be obtained through the carbonylization of benzyl halides with the sodium salt of cobalt octacarbonyl (R. F. Heck et al., J. Amer. Chem. Soc. 85, (1963) 2779-82, and French Patent No. 1,313,306 of 1962). The use of the sodium cobalt carbonyl is extremely difficult technically and also provides poor yields. Phenylacetic acid esters are also accessible via the carbonylization of benzyl halides with CO under pressure in the presence of rhodium complexes (K. Ohno et al., J. Amer. Chem. Soc. 90, (1968) 99-107). Again, poor yields are obtained by this process, which has to be performed at higher pressures (100 atm.).
According to a new method of preparing phenylacetic acid esters, benzyl chloride is brought to reaction in polar solvents such as dimethyl formamide or dimethyl sulfoxide with carbon monoxide and alcohol in the presence of nickel tetracarbonyl and iodine as catalyst and in the presence of alkaline earth oxides as HCl acceptors (German "Offenlegungsschrift" 1,914,391). The disadvantages of this process result from the large amounts of nickel carbonyl and iodine that are needed as catalysts, and from the recovery of the expensive solvents used. On the basis of the long reaction time of 26.5 hours poor unit-volume yields are obtained, which make the process uneconomical.